This application is based on Japanese Patent Applications No. 2000-086158 filed Mar. 27, 2000, the contents of which are incorporated hereinto by reference in its entirety.
1. Field of the Invention
The present invention generally relates to a vibration damper installed in a vibrative member of a vehicle, for reducing or attenuating vibration of the vibrative member. More particularly, the present invention is concerned with such a vibration damper which is novel in construction and which is suitably applicable to vibrative members such as suspension arms, sub frames, body panels, mounting brackets, and vibrative members used in an engine unit or an exhaustion system, so that the vibration damper exhibits an excellent damping effect with respect to vibrations excited in these vibrative members.
2. Description of the Related Art
As vibration damping means for damping or reducing vibration excited in vehicles such as an automotive vehicle, there are known (a) a mass damper wherein a mass member is fixed to a vibrative member, (b) a dynamic damper wherein a mass member is supported by and connected to the vibrative member via a spring member and (c) a damping material which is a sheet-shaped elastic member and secured to the vibrative member. However, these conventional devices suffer from various potential problems. For instance, (a) the mass damper and (b) the dynamic damper both require a relatively large mass of the mass member, and exhibit desired vibration damping effect only to significantly narrow frequency ranges. (c) The damping material suffers from difficulty in stably exhibiting a desired damping effect, since the damping effect of the damping material is prone to vary depending upon the ambient temperature.
The present assignee has been disclosed in International Publication WO 00/14429 a novel vibration damper used for an automotive vehicle, which includes a housing member having an inner space and fixed to the vibrative member, and an independent mass member which is accommodated in the inner space of the housing member without being bonded to the housing member, so that the independent mass member is displaceable or movable relative to the housing member, while being independent of the housing member. In the disclosed vibration damper, the independent mass member is forced to move into and impact the housing member, upon application of a vibrational load to the damper, whereby the vibration of the vibrative body is effectively reduced or absorbed based on loss or dissipation of energy caused by sliding friction generated between the abutting surfaces of the mass member and the housing member and caused by collision or impact of the independent mass member against the housing member. This proposed vibration damper is capable of exhibiting a high damping effect over a sufficiently wide frequency range of frequency of input vibrations, while having a relatively small mass of the mass member.
In order to stably establish a desired damping effect of the vibration damper disclosed in the above-indicated document, it is required that the independent mass member is brought into impact directly against the housing member in a vibration input direction in which vibrations to be damped is applied to the vibration damper. In the case where the vibrational loads are applied in various vibration input directions to the vibration damper, for example, there is a need for disposing the independent mass member in the accommodation space such that the independent mass member is movable or displaceable relative to the housing member in every vibration input direction.
In order to stably exhibit a desired damping effect, the vibration damper is further required to effectively provide a bouncing displacement or movement of the independent mass member in the accommodation space, upon application of a vibrational load to the vibration damper, whereby the independent mass member is repeatedly brought into impact on and bounce off the housing member so as to repeatedly apply impact energy to the housing member. To meet this end, there is a need for reducing friction at an interface formed between the independent mass member and the housing member upon abutting or sliding contact of the independent mass member with the housing member.
In order to stably establish the desired damping effect of the vibration damper, there is yet further required to stabilize the condition of the impact between the independent mass member and the housing member. For instance, it should be stabilized an abutting portion or an abutting surface area of the independent mass member at which the independent mass member impacts on the housing member.
It is therefore an object of this invention to provide an improved vibration-damping device for vehicles capable of exhibiting a desired damping effect with respect to vibrations applied thereto in a plurality of vibration input directions.
It is another object of this invention to provide an improved vibration-damping device for vehicles, which permits a decreased friction at the interface formed between the independent mass member and the housing member, upon abutting or sliding contact of the independent mass member with the housing member, leading to decrease in frictional resistance to the displacement of the independent mass member. This vibration damping-device therefore facilitates the bouncing displacement of the independent mass member relative to the housing member, thereby exhibiting an improved vibration damping effect.
It is yet another object of this invention to provide an improved vibration-damping device for vehicles capable of exhibiting a desired damping effect with high stability, owing to stabilized condition of impact of the independent mass member on the housing member.
The above object may be achieved according to the principle of the present invention, which provides a vibration-damping device for damping vibrations of a vibrative member of a vehicle, comprising: (a) a rigid housing member formed integrally with or independently of the vibrative member and being subjected to the vibrations of the vibrative member, the housing member defining an accommodation space; and (b) an independent mass member having a spherical outer surface and disposed non-adhesively in the accommodation space such that the independent mass member is opposed to an inner surface of the housing member defining the accommodation space, with a spacing therebetween, and is displaceable relative to the inner surface of the housing member. The independent mass member and the housing member are brought into direct and elastic impact against each other at respective abutting surfaces thereof in at least one vibration input direction, upon application of the vibrations in the at least one vibration input direction.
In the vibration-damping device of the present invention constructed as described above, the independent mass member has the spherical outer surface. This arrangement makes it possible to arrange the independent mass member to directly and elastically impact against the housing member in a plurality of optional vibration input directions, by only adjusting suitably the configuration of the accommodation space defined by the inner surface of the housing member. Therefore, the vibration-damping device can exhibits an excellent damping effect with respect to vibrations applied in the plurality of vibration input directions.
In the vibration-damping device of the present invention, the independent mass member is brought into abutting or sliding contact with the housing member with a relatively small contact area, owing to its spherical outer surface, leading to a low resistance to the displacement of the independent mass member. For instance, the independent mass member is less likely to be caught in the housing member during its bouncing displacement within the accommodation space of the housing member. This arrangement facilitates the bouncing movement of the independent mass member in the accommodation space of the housing member, whereby the vibration-damping device can exhibit an excellent damping effect with high efficiency, based on the impact or abutting contact of the independent mass member on or with the housing member.
Moreover, the independent mass member having the spherical outer surface permits an elimination of a directional restriction of the independent mass member in the accommodation space, resulting in stabilized condition of the impact of the independent mass member against the housing member. Thus, the vibration-damping device can damp the vibrations of the vibrative member with high stability.
The housing member may be made of metallic materials such as iron or an aluminum alloy, or a synthetic resin material, for example. Preferably, the housing member may be formed of a rigid material having a modulus of elasticity of 5xc3x97103 MPa or more so as to establish a required hardness enough to support the independent mass member and a desired damping effect. Alternatively, the housing member may be made of a foamed body of the rubber or synthetic resin materials. In order to reinforce the independent mass member formed of the elastic body or the formed body, it may be possible to bond a rigid members made of metal to the independent mass member.
It may also be possible that the independent mass member may comprise a mass body formed of rigid materials having a relatively higher gravity such as metal or stones. In the case, at least one of the abutting surfaces of the independent mass member and the housing member is covered by an elastic body layer made of a rubber material or a synthetic resin material, which is formed on and secured to the at least one abutting surfaces.
According to one preferred form of the invention, the independent mass member includes a solid metallic mass body and an elastic body layer formed on and secured to the entire outer surface of the metallic mass body. In this arrangement, the independent mass member is likely to receive the impact load at various points evenly spread over the outer surface of the elastic body layer, owing to the rotation of the independent mass member in the accommodation space, thereby avoiding application of the impact load to only a local portion of the elastic body layer, resulting in improved durability of the elastic body layer and a resultant improved durability of the vibration damping device.
According to another preferred form of the invention, at least one of the abutting surfaces of the housing member and the independent mass member has a Shore D hardness of not greater than 80. This arrangement is effective to assure an improved damping effect of the present vibration-damping device and a reduced impact noise upon impact of the independent mass member with the housing member. For instance, the elastic body layer formed on and bonded to the at least one of the abutting surfaces of the independent mass member and the housing member may preferably have a Shore D hardness of 80 or lower, more preferably, within a range of 20-40, as measured in accordance with ASTM method D-2240. For the above-mentioned improved damping effect and the reduced impact noise, at least one of the abutting surfaces of the independent mass member and the housing member, which is preferably formed of the elastic body layer, is also arranged to have a modulus of elasticity within a range of 1-104 MPa, more preferably, 1-103 MPa, and a loss tangent is not less than 10xe2x88x923, more preferably within a range of 0.01-10, preferably.
According to a further preferred form of the invention, the abutting surface of the independent mass member and the abutting surface of the housing member are spaced apart from each other by a distance within a range of 0.05-0.8 mm, more preferably 0.05-0.5 mm, and the independent mass member may be reciprocally movable by a distance within a range of 0.1-1.6 mm, more preferably within a range of 0.1-1.0 mm, between at least two abutting surfaces of the housing member which are opposed to each other with the independent mass member therebetween, in the at least one vibration input direction. This arrangement is effective to establish further improved damping effect of the vibration-damping device of the present invention.
According to a still further preferred mode of the invention, the housing member is made of a rigid material such as a synthetic material, which has a modulus of elasticity within a range of 5xc3x97103-5xc3x97104 MPa. This results in a minimized impact noise and an ease of tuning of damping characteristics of the vibration-damping device. In the case where the housing member has a relatively low rigidity, the abutting surfaces of the independent mass member and the housing member may be suitably arranged to have a modulus of elasticity which is smaller than that of the housing member. More preferably, the modulus of elasticity of the abutting surfaces of the independent mass member and the housing member are held within a range of 1-102 MPa. This arrangement makes it possible to assure a desired strength and durability of the housing member, and to improve a damping effect of the vibration-damping device with respect to low frequency vibrations, for example.
The configuration of the housing member is not particularly limited. Various configurations may be applicable to the housing member, taking into account the vibration input directions in which vibrations to be damped are applied to the damping device. In a yet further preferred form of the invention, the accommodation space of the housing member has a circular configuration in cross section. In a still another preferred form of the invention, the accommodation space of the housing member has a square configuration in cross section.
When the accommodation space of the employed housing member has a spherical configuration as a whole, i.e., has circular cross sectional shape in all sections, the spacing between the spherical outer surface of the independent mass member and the spherical inner surface of the housing member is made substantially constant in all directions, whereby the vibration-damping device can exhibit an excellent damping effect with respect to all vibrations applied in any vibration input directions. When the accommodation space of the employed housing member has a cube shape, the independent mass member is opposed to each of six plane surfaces of the cubic housing with a substantially constant spacing therebetween. Namely, the independent mass member is reciprocally movable or displaceable by a substantially constant distance between two of the six plane surfaces opposed to each other in each of three directions of axes of the independent mass member, which axes are intersect each other at right angles. Thus, the vibration-damping device can exhibit an excellent vibration damping effect with respect to vibrations applied in the three axial directions. It is noted that the use of the non-spherical accommodation space, such as the cubic accommodation space, permits the independent mass member to impact on or sliding contact with the housing member with a decreased contact area, thereby facilitating further the bouncing displacement of the independent mass member relative to the housing member upon application of the vibrations to the vibration-damping device.
According to a still further preferred form of the present invention, the accommodation space comprises a longitudinal space extending in a longitudinal direction with a constant cross sectional shape, and accommodates a plurality of the independent mass members which are arranged in series in the longitudinal direction. The center axis of such an accommodation space in the form of the longitudinal space may extend straightly or curvedly in the longitudinal direction. The adoption of the longitudinal accommodation space permits an effective arrangement of the plurality of the independent mass members with ease, according to a configuration of a portion of the vibrative member to which the vibration-damping device is installed.
Further the structure of the housing member is not particularly limited. In still another preferred form of the present invention, the housing member is formed of a metallic material by extrusion, and having a bore extending therethrough in an extruding direction, the bore of the housing member defining the accommodation space. The optional number of the bores may be formed in the housing member. If the only one bore is required, a hollow pipe member may be used as the housing member. For instance, a hollow arm as the vibrative member may constitute the housing member. Alternatively, a panel structure having a plurality of the bores juxtaposed with each other may be usable as the housing member. For instance, a floor panel as the vibrative member may constitute the housing member.
According to yet another preferred form of the invention, the single independent mass member is desirably arranged to have a mass within a range of 10-1000 g, preferably 50-500 g. With the mass of the independent mass member to 1000 g or smaller, more preferably 500 g or smaller, the independent mass member is prone to be excite to its bouncing movement or displacement with ease and efficiency, upon application of the vibrational load to the vibration-damping device. With the mass of the independent mass member set to 10 g or larger more preferably 50 g or larger, the vibration-damping device ensures its damping effect based on the impact of the independent mass member on the housing member.
According to a still yet further preferred embodiment, a total mass of the independent mass member is held within a range of 5-10% of the vibrative member. Namely, if the mass of the independent mass member is smaller than 5% of the mass of the vibrative member, the vibration-damping device possibly suffers from difficulty in exhibiting a desired damping effect, and if the mass of the independent mass member is larger than 10% of the mass of the vibrative member, the vibration-damping device suffers from a problem of increase in the overall weight of the device. If the plurality of independent mass members are accommodated in the accommodation space, the total mass of the plurality of independent mass members is desirably arranged to be held within a range of 5-10% of the mass of the vibrative member.